Gear



July 9,1946.

GEARS Filed April 14, 1944 l f INVHVTOR.

. portions I6 and I1 having different radii.

Patented July 9, 1 946 oFFicE GEAR Francis H. Boor, Lafayette, Ind.,assignor to Fairfield Manufacturing Company Application April 14,*1944,Serial No. 530,997

5 Claims.

1 My invention relates in general to gear wheels and more particularlyto gear wheels adapted to rotate primarily in one direction.

With gears that rotate primarily in only one direction, importantadvantages over conventiona1 involute design in teeth are obtained by myinvention.

An object of my invention is to increase the base tooth thickness ofgear teeth without decreasing the total number of teeth on a given gear.

Another object of my invention is to increase the number of teeth on agiven gearand still retain a wide tooth base.

Another object of my invention is to decrease the stress per tooth on agear having a given number of teeth.

Another object of my invention is to increase Vthe tooth contact ratiofor a gear without decreasing the base tooth thickness.

Another object of my invention is to reduce the stress concentration inthe fillet of the tooth on the active, or drive side of the tooth.

Other objects and a fuller understanding of my invention may be had byreferring to the following description and claims, taken in conjunctionwith the accompanying drawing, in which the single figure of the drawingrepresents a fragmentary view of a gear embodying the features of myinvention.

With reference to the drawing, I illustrate a fragmentary portion of agear having a plurality of teeth. The teeth are all alike and thedescription will deal with the tooth 8. The tooth 8, developed inaccordance with my invention has two involute curved surfaces, one ofthe surfaces being designated by reference character I generated from abase circle I I, and the other of the surface is designated by referencecharacter I2 and is generated from a base circle I3. The tooth also hasa top land surface I4 and is separated from adjacentteeth'by a bottomAland surface I5 which is composed of two curved fillet The tooth face I0blends with the bottom land surface I5 which is between adjacent teeth,through the fillet portion I6 at the base of surface I0 and the toothface I2 blends with the bottom land surface l5 through the filletportion I1 lat the base of lsurface I2. Point I is the center of thetooth, as the distance from I to 3 equals the dis,- tance from I to 2.Line frepresents the tooth center line.

In certain designs, gears ina' given device ro-v tate in only onedirection and therefore, have sctive contact on only one side of anygiven tooth. In my invention the gear teeth for gear wheels adapted torotate primarily in one direction are designed whereby a. standardinvolute surface is maintained on the drive or load carrying side of agiven tooth, but have a backing or reverse side with a more slopingsurface. Such a design provides a tooth base of greater width, andtherefore, greater strength, than a standard involute tooth, orconversely, a greater number of teeth per gear for a given tooth basethickness, thereby providing a greater contact ratio between matinggears. Also in my invention the large fillet I6 on the drive side of thetooth and a small fillet I1 on the reverse side, results in a strongertooth.

In the drawing, the surface I0 is a standard involute surface definedfrom the base circle I I. A base circle is the circle from which theinvolute in the plane of rotation is generated.

The surface I2 is the surface of the tooth 8 not carrying an activeload. 'I'he surface I2 is an involute curve and is defined from a basecircle I3 which is of a smaller diameter than base circle II. of astandard involute tooth as defined by common practice, the commonpractice being to define both surfaces of a tooth from a common basecircle with the tooth being symmetrical about the tooth center line 4.Thus, the increase of tooth base'thickness brought about by my inventionis indicated by the distance 26 between the dot-dash line 21 and theinvolute surface I2. The increase 26 of the base tooth thicknessprovides teeth which are stronger than standard involute gear teethWithout reducing the total number of teeth on a given gear.

The surface I2 is disposed to contact a similarly defined mating surfaceof a meshing gear tooth, and I illustrate a line of action I 8 passingthrough the pitch point 3. y

The line of action I8 and the pitch line 22 intersect each other, thepoint of intersection being at the pitch point 3, and form an includedangle 2I therebetween. The line of action 24 and the pitch line 22intersect each other, the point of intersection being at the pitch point2, and form an included angle 23 therebetween. The pitchv line 22 isdisposed to intersect the tooth 8 at pitch points 2 and 3. A radial line4 of the tooth B'intersects the pitch line 22 at 9. point I which is atthe center of the tooth along the pitch line 22 inasmuch as the distancefrom they The dot-dash line 21 indicates the position drawing, however,that the tooth is unsymmetrical about the radial line 4. symmetrical,lines I8 and 24 would intersect on center line Il. The angle 23 issmaller than the angle 2l. The effect of having angle 23 smaller thanangle 2l is to provide a larger contact ratio between the driving facesof the meshing gear teeth, resulting in quiet operation, with a widetooth base. In accordance with accepted terminology, the portion of thetooth surfaces above the pitch line 22 may be referred to as the face,"and the portion below the line 22 as the flank Tooth failure is oftencaused by a concentration of stress at the base of the tooth on thedrive side in the fillet area I6 of the bottom land l5. With teethdeveloped according to my invention, a longer radius 28 is used todefine fillet portion iii than is used in standard practice. The filletportion il is defined by a radius 29 of standard or minimum length. Thelarger fillet i6 resulting from the use of a long radius 26 increasesthe strength of the teeth. The broken line 3E represents the standard orconventional shaped n1- let, that is, line 3o would have the same radiusas line Il, and the bottom land I5 would be symmetrical about a toothspace center line d. In my invention radius 23 is larger than ispossible to have when the tooth 4space is symmetrical.

Although 1 have described my invention with a certain degree ofparticularity, it is understood that the present disclosure has beenmade only by way of example and that numerous changes in the details ofconstruction and the'combination and arrangement of parts may beresorted to without departing from the spirit and the scope of theinvention as hereinafter claimed;

I claim as my invention:

1. A gear wheel having a plurality of teeth,

i each of said teeth being unsymmetrical and having sides describinginvolute profiles defined from If the tooth were a base circle, the basecircle for said drive side base circles, one of said sides being definedfrom a base circle of smaller diameter than the other, the side definedyfrom the base circle of smaller diameter, when in contact with a similarside of a tooth of another gear, having a line of action inclined at agreater angle to a pitch line of thel gears than the line of action ofthe side of said tooth defined from the larger of said base circles,

said sides of adjacent teeth being separated by a-` bottom landlportion, said bottom land portion being unsymmetrical with respect to aradial line of the gear, portions of said bottom land being defined fromdifferent radius centers, and the longer of the radii defining the proleline of the bottom land area adjacent to the side of said toothhavingthe larger of said lines of action.

2. A gear wheel having a plurality of gear teeth, each of said gearteeth having a curved drive side surface including a face portion and aflank portion, and a. curved reverse side surface including a faceportion and a flank portion, at least said flank portion of the driveside surface having a profile which defines an involute curve developed'from a base circle, and at least said flank portion of the reverse sidesurface having a profile which denes an involute curve developed from abase circle, the base circle for said drive side surface being oi alarger diameter than the said circle for said reverse side surface.

surface being of a larger diameter thanthe base circle for said reverseside surface, said drive side surface of each tooth being adjacent tothe reverse side of a neighboring tooth, said drive side surface andreverse side surface of the neighboring teeth being joined in a bottomland area, said bottom land area having a first surface portion and asecond surface portion, said first surface portion having a radius, saidsecond surface p0rtion having a radius,said first portion radius beinglonger than the said second portion radius, and said first surfaceportion being joined to the profile of the said flank portion of thedrive side surface and the said second surface portion being joined tothe profile of the said shank portion of the reverse side surface of theneighboring tooth.

4. A gear Wheel having a plurality of gear teeth, eachof said gear teethhaving a curved drive side surface including a face portion and a flankportion, and a curved reverse side surface including a face portion anda anlrv portion, at least said flank portion of the drive side surfacehaving a profile which defines an involute curve, and at least saidflank portion of the reverse side surface having a profile which definesan involute,

first portion radius being longer than the said sec-f ond portionradius, and said first surface portion being joined ot the profilel ofthe said ank portion of the drive side surface and the said secondsurface portion being joined to the profile of the said shank portion ofthe reverse side surface of the neighboring tooth.

5. A gear wheel having a plurality of gear teeth. each of said gearteeth havinga curved drive side surface including a face portion and aflank portion, and a curved reverse side surface including a faceportion and a anlr portion, said face and flank portion of the driveside surface comprising a continuous involute surface having a profilewhich defines an involute curve developedd'rom a base circle, and saidface and nani: portion of the reverse side surface comprising acontinuous surface having a profile which defines an involute curvedeveloped from a base circle, the base circle of said drive side surfacebeing of a larger diameterv than the base circle for said reverse sidesurface.

FRANCIS H. BOOR.

